Are Raccoons On The Road To Domestication?

Recent studies on raccoons and dark-eyed juncos investigate how urban wildlife is evolving.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:03Flora Lichtman?

  I'm Flora Lixman and you're listening to Science Friday. First, there was Pizza Rat, then Central Park's Celebrity Coyote, and finally, I give to you Drunk Raccoon.

• 0:15Speaker 01

  A now infamous raccoon. Video obtained by NBC News shows the critter inside a Virginia liquor store. A trashed panda splayed out next to a trash can and toilet, like that one person that maybe had one too many at the holiday party.

• 0:29Flora Lichtman?

  And there might be more to this ridiculous story than amazing memes. This raccoon points, with its tiny little adorable hands, to a possible larger trend. A new study shows that raccoons are showing signs of being domesticated. Today, we are talking about that and what it means to be a wild animal in a world dominated by one animal in particular: us. Here to discuss are Rafaela Leish, a biologist studying raccoons at the University of Arkansas at Little Rock, and Pam Ye, an evolutionary biologist studying birds, among other creatures, at UCLA. Welcome to you both to Science Friday.

• 1:07Speaker 02

  Hi. Thank you for having us.

• 1:09Speaker 03

  Yeah, thank you so much.

• 1:11Flora Lichtman?

  Rafaela, let's start with that raccoon that lived its best life in the Virginia liquor store.

• 1:15Speaker 02

  Yeah.

• 1:16Flora Lichtman?

  When you saw that story, as someone who studies raccoon domestication, what did you think?

• 1:22Speaker 02

  So, I actually, I got an email. A news agency was asking me for comment on that. And I was like, I'm not sure what to say, other than, I'm pretty sure it was fairly drunk. But, yeah, that was honestly perfect timing for our study. It almost seemed like we paid off that raccoon to, like, break into a liquor store right after our paper came out. Yeah.

• 1:47Flora Lichtman?

  I mean, OK, so what are the signs that... What are the signs that raccoons are getting domesticated?

• 1:54Speaker 02

  Yeah, so I got to preface this by saying that there's like basically we found one trait that could be associated with a domestication phenotype. We can't clearly say that they really are on the pathway to domestication, but we can kind of use that as an indication of them potentially being on the path of domestication. So what we found was that urban raccoons have shorter snouts than raccoons that live on the countryside. And this reduction in snout length is a trait that we very commonly see in domesticated animals. And it's part of what we call the domestication syndrome. So a whole collection of traits that we very much associate with an animal being domesticated, like floppy ears, curly tails, white patches, smaller brains, and shorter snouts.

• 2:40Flora Lichtman?

  Smaller brains?

• 2:41Speaker 02

  Yeah, yeah. Which it doesn't automatically mean that they're dumber, because there was a study we published on on cat brains, and domesticated cats have smaller brains than wild cats. And I had-

• 2:52Flora Lichtman?

  Yeah, watch out. We have like really a lot of team cat people at this point.

• 2:56Speaker 02

  Yeah, exactly. So I just wanted to say like, we never said domesticated cats are dumber, because it was just about pure brain volume. It could, you know, it doesn't have to mean anything in regards to intelligence necessarily. But yeah, all of those things are traits we associate with domesticated animals.

• 3:11Flora Lichtman?

  But why does snout size, why should that correlate with whether an animal is domesticated?

• 3:15Speaker 02

  So there's one hypothesis, and I'm, I want to walk you through this hypothesis, but keep in mind, we're still arguing whether this is the thing or not, whether it's like true or not. But the main thought that we have is, all these traits that we see in domestication syndrome, potentially could be explained by a mechanistic pathway in the early development. So if you think about the journey of a domesticated animal, at the very beginning stages, they have to adapt to living in close proximity to humans. So they undergo a fairly strong selection pressure for friendly and tolerant behavior, because usually animals, when they live close to us, you know, if you, if you're too aggressive,

• 3:56Speaker 02

  then you usually get eliminated from the breeding population. So animals that are tolerant and can make best use of that human environment can reproduce more. So over time, you have this, what we call, selection pressure for tameness. And this hypothesis, the neural crest domestication syndrome hypothesis, suggests that the selection for tameness alters the migration and proliferation of neural crest cells. Those are cells that are very important in development and provide a lot of ancestral cells for different organ systems. So that has the potential to explain all of these traits that we observe across the phylogenetic tree of domesticated animals.

• 4:38Flora Lichtman?

  Wait, let me see if I understand. So if you start behaving tamely, somehow that is linked to an embryonic development stage that also changes the size of your nose?

• 4:50Speaker 02

  So it's kinda, it's really like, oh, think about it as like a really a multi-generation thing. So that's not something that happens super fast, but would be a very slow process where basically over many generations, these traits basically get reinforced and then show up as this domestication syndrome.

• 5:10Flora Lichtman?

  Pam, how do we define domestication?

• 5:13Speaker 03

  Oh, that's a good question. You know, we have these wild animals and their closeness with humans in terms of their proximity starts to change their behaviors, change their morphology, change their genes, because their selection for the one that ones that happen to be tamer, the ones that happen to have the traits that humans find appealing or find useful. Raffaela, you might have a better.

• 5:42Speaker 02

  I, I, I was really interested to hear your take on it because the definition of domestication is like, that's actually a really, really difficult question. There's a bunch of new research that came out where we basically argue back and forth. And that's kind of like the fun, the sweet spot of science, right? When you have these like back and forth arguments of what is domestication? How do you define it? Because of course you have the aspects of us like selecting, like actively selecting and breeding, but then you also have aspects of really like these very beginning stages where animals like get used to a human environment. And that, that doesn't necessarily have to end up in a domesticated product. And I think there's kind of like a more of a spectrum really of like, where do animals end up on that spectrum? But yeah, the definition is actually really kind of tricky. And just

• 6:26Speaker 02

  in the last 12 months, there have been a bunch of papers that came out arguing back and forth on how we define these things, because some definitions, for example, would consider, I think, bedbugs to be domesticated, but.

• 6:40Speaker 02

  And I hope I hope I remember this correctly, but how sparrows to not be domesticated. So it is really tricky to find a definition that encompasses this kind of fairly complex interaction and and setup of what it means to live in close proximity to humans.

• 6:59Flora Lichtman?

  Pam, you had a recent study on on the songbird, the dark eyed junko. So introduce us to them and what their life is like in terms of the ones that you studied.

• 7:10Speaker 03

  Yeah, so the dark eyed junko is a small passerine. It's an unshrieked sparrow and they typically they're found actually in many places in the US, so they're a very common species. But they're typically found at altitude in the mountains in in forest habitat. About maybe 50 years or so, they colonized an urban area in Southern California, which is the campus of UC San Diego. And so it's been almost 30 years now since I started studying those guys as a graduate student. And, you know, because they were here and my advisor said, you know, there's something interesting going on, you're going to find interesting evolution because this is such

• 7:55Speaker 03

  a different environment, you know, or or we should at least look, you know.

• 7:59Flora Lichtman?

  From where they live in the wild.

• 8:01Speaker 03

  From where they live in the wild. They're very, very different. And of course, you know, when you get into this type of field, you want to go out to, you know, you want to go to the Himalayas, you want to go to Antarctica, you want to go far away. And I was not excited at first about this, but they have turned out to be such an interesting species and an amazing set of populations. And they have colonized San Diego, but then they've colonized other Southern California urban areas over the last few decades. And so now we have multiple, as far as we can tell, fairly separate urban populations with minimal gene flow. And so that allows us to ask some questions about generalizations we can make about urban evolution.

• 8:45Speaker 03

  Like, are each of these populations evolving in the same way? Are they evolving in different ways? What are the important selection pressures?

• 8:52Flora Lichtman?

  Okay, so you you studied these birds during the lockdown.

• 8:58Flora Lichtman?

  What did you find?

• 9:00Speaker 03

  We found that the birds that were born in the years where we didn't have a lot of people on campus actually had longer, skinnier beaks than the ones that were either born before the pandemic or born, you know, 2022, 23, 24 afterwards. It turned out that the ones that were born during the 2020 and 2021 campus closures had beaks that looked more like the wildland beaks, that were longer and skinnier, more slender.

• 9:30Flora Lichtman?

  Why would that be?

• 9:32Speaker 03

  That is a very good question. And we think it has to do with the food on campus. We have a lot of students on campus, people, faculty, staff. And so, and everyone is eating and there's trash, you know, overflowing in the trashcan sometimes. And, and, you know, we leave crumbs everywhere. And I think that there was strong selection pressure during normal times for birds that had, that had shorter beaks, they probably were able to get at more of that food.

• 10:00Flora Lichtman?

  Short beaks are good for trash?

• 10:02Speaker 03

  We think so.

• 10:03Flora Lichtman?

  Okay.

• 10:04Speaker 03

  We think so. I think that they're, I think that they're good for a kind of a generalist, being able to grab at the food that we produce. We don't know for sure, so I think that would be like an important thing to test. But, but that seems to be the case, that they can handle more of the odd sized and variable shaped food a little bit more easily. Whereas during the pandemic, when there were, there was way less food on campus, birds were, Jungkook's are typically guanabores, they eat a lot of seeds, they feed their offspring insects. And so you often see them digging in lawns and vegetation, looking for insects or, you know, getting, getting the seeds. And we think that those long slender beaks do better with insects and grains.

• 10:47Speaker 02

  Pam, can I, can I ask you a question? Sorry, Florid, I don't want to interrupt, but this is super interesting. Like, do you think that this could also be like a plastic response to what the birds are exposed to early on?

• 11:00Speaker 03

  Yeah, that's a good question. So there, and, and so that's why we, we have to be a little hesitant when we say of, you know, rapid evolution, you know, as a result of the pandemic, because it could be a plastic trait. It could be.

• 11:12Flora Lichtman?

  When you say a plastic trait, you mean that it, it's basically a trait that is adaptable based on the, the environment that they're in, right?

• 11:19Speaker 03

  Exactly.

• 11:19Flora Lichtman?

  Like it can change during their life.

• 11:20Speaker 03

  Exactly, exactly, exactly. And so we can't fully rule that out, but. But we know in general for birds, there are beaks, there are genes that are related to all these beak traits. And so we think that this is one of those things that doesn't change that much. But I think it's something we probably need to, it would be nice to look into more.

• 11:44Flora Lichtman?

  Don't go away, because when we come back, Raffaela, I want to hear when I can expect to have a pet raccoon.

• 11:49Speaker 03

  Sounds good.

• 11:50Flora Lichtman?

  And whether I can look forward to a raccoon doodle, a raccoon frieze, an English cockercoon.

• 12:00Speaker 03

  I love it.

• 12:08Speaker 04

  Science Friday is supported by PBS, presenting Going Wild. If you love learning about the natural world and meeting the scientists who help us understand it, be sure to check out the new season of Going Wild with Dr. Ray Wynn Grant. It's the chart-topping and Webby Award-winning podcast from the folks at Nature on PBS, now with a video companion series. In this season of Going Wild, host acclaimed wildlife ecologist Dr. Ray Wynn Grant heads out into the field to explore the animals, people, and stories that make nature worth saving. Stops include a hibernating black bear den in Arkansas and an underwater shipwreck site off the Florida coast. If you're looking for a place to start, check out the season's debut episode, where Ray joins beloved biologist and influencer Jordan King in the Florida Everglades

• 12:52Speaker 04

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• 13:33Speaker 04

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• 13:40Speaker 05

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• 13:54Flora Lichtman?

  We're back. I'm talking with biologist Rafaela Lesh and Pamela Yay about urban wildlife and how these creatures are becoming a little less wild. So Rafaela, we know with dog domestication that, you know, phase one with wolves was sort of wolves eating our scraps. And I guess, you know, these days, a lot of animals are living beside us, rats, bears, possums. Is there something else about an animal that makes it prone to domestication?

• 14:28Speaker 02

  Yeah, so you're, you're, you're asking all the, the big questions, which like is really good. So we have some thoughts on what might kind of like increase the probability of like an animal falling down that hole of like the domestication pathway. So they have to have a social system that kind of has enough complexity in it that would kind of like benefit a coexistence between these animals and us. Also, the animals have to be animals that are not super dangerous to us humans. So bears, for example, would most likely never end up on the pathway to domestication, simply because they're, they

• 15:11Speaker 02

  are too dangerous to really create this environment of like, you know, a human environment and all of that. So there's certain limitations-

• 15:18Flora Lichtman?

  But wolves are dangerous to us, right?

• 15:20Speaker 02

  Well, I mean, they're kind of like, usually they, like, wild wolves are really kind of like, they try to stay, stay away from humans. So they're really, I guess they could be dangerous if you, you know, if you really pushed the wolf to its limits, but they're not really out to like get humans. That's not really-

• 15:40Flora Lichtman?

  Eat us.

• 15:40Speaker 02

  Yeah, exactly. Yeah, we're not on the menu. Of course, like nutrition dietary background could make a huge difference. One thought, for example, that we had is that animals that are able to exploit the human trash that we have laying around- Um. Because they have somewhat of a match with their dietary background. Um. Would have an easier time being domesticated. So if we look at dogs, for example, they have um. The ability to digest starch a lot more than wolves do. So they clearly adapted to kind of like going through our trash and you know. Eating whatever bread and carbohydrates we throw away. So animals that are able to kind of thrive on what we throw away.

• 16:23Speaker 02

  Potentially have an easier time going down that pathway. But now, if you think about cats. They don't really do carbohydrates to the same degree that like dogs can. Um. There you have an argument that the trash that we have attracts rodents. So cats might have. Um. It kind of like exploited the rodents on the trash. So we were thinking that. Uh. Or the initial thought behind looking at raccoons was, well. We know they're there. We know that every single trash can or every single dumpster on campus. Um. Houses raccoons. Um. So it was kind of interesting to look and see. Um. If there was a pattern that would hold across the entirety of the United States.

• 17:01Flora Lichtman?

  Raphael, how long till I have a raccoon sleeping at the foot of my bed?

• 17:04Speaker 02

  Oh, yeah, that. And see, this is where the bad, bad news comes in. I'm so sorry. And I wish time travel was a thing because it definitely would not be in a human lifetime. So. If they are in the pathway to domestication. Um. It would most likely be similar to other animals like thousands of years, so many, many generations before we end up with like. A version of this animal that could be considered domesticated. Um. And there's also another thought that we have where we kind of want to confirm our finding, and that is. Because it ties in so nicely with what Pam said earlier. About like dietary impacts on like morphology and anatomy. So we just looked at this change in snout from like a perspective of.

• 17:50Speaker 02

  A domestication framework. But um. We also need to consider that potentially there could be. A difference in in dietary background in all of these populations. And we have to test out and rule out that that's not a signal that we're picking up. Um. I don't think it is, but you know, that's the joy of science. It doesn't matter what I think. We're gonna need data for that.

• 18:13Flora Lichtman?

  This is a tiny bit philosophical, but do you both have feelings about wild animals becoming more dependent on people?

• 18:20Speaker 03

  Yeah, I think sometimes people think about humans as one thing, and then there's nature and there's us, but we're really very much a part of the ecosystem and the animals affect us and we affect other animals. So, you know, we really need to be aware if we want to think about how we want to change things or how we are trying not to change things.

• 18:41Speaker 02

  The fact that our cities keep encroaching, we keep encroaching into wildlife and kind of like true wild environments, if we do that, it's almost inevitable that animals will adapt to us. Like, at the end, we're also like ecosystem engineers, right? So wherever we go, we change things. And I think that has to be a very conscious thing that we have to consider as humans. How do we deal with that?

• 19:06Flora Lichtman?

  Pam, Rafaela, thank you so much for talking to me today.

• 19:09Speaker 02

  Thank you.

• 19:09Speaker 03

  Thank you so much. Thanks for having us.

• 19:12Flora Lichtman?

  Rafaela Leish is an assistant professor of biology at the University of Arkansas, Little Rock, and Pam Ye is a professor of ecology and evolutionary biology at UCLA.

• 19:24Flora Lichtman?

  This episode was produced by Kathleen Davis and Dee Peterschmidt. Thank you for listening. And if you have an urban wildlife encounter that you want to share, or tell me what wild animal is on your domestication wish list, I'd love to hear from you, 877-4SYFRI. I'm Flora Lichtman. See you next time.